Organic electronic devices (OED)s are articles that include layers of organic materials, at least one of which can conduct an electric current. Illustrative examples of known OED constructions include photovoltaic devices, rectifiers, transmitters, and organic light emitting diodes (OLED)s.
An organic light emitting diode (OLED) is a typical example of an OED. OLEDs, sometimes referred to as lamps, are desirable for use in electronic media because of their thin profile, low weight, and low driving voltage, i.e., less than about 20 volts. OLEDs have potential use in applications such as backlighting of graphics, pixelated displays, and large emissive graphics.
OLEDs typically consist of an organic light emitter layer and additional organic charge transport layers on both sides of the emitter, all of which are sandwiched between two electrodes: a cathode and an anode. The charge transport layers comprise an electron transporting layer and a hole transporting layer. Charge carriers, i.e., electrons and holes, are injected into the electron and hole transporting layers from the cathode and anode, respectively. Electrons are negatively charged atomic particles and holes are vacant electron energy states that behave as though they are positively charged particles. The charge carriers migrate to the emitter layer, where they combine to emit light.
Examples of OLEDs include molecularly doped polymer devices where charge carrying and/or emitting species are dispersed in a polymer matrix (see J. Kido, “Organic Electroluminescent devices Based on Polymeric Materials,” Trends in Polymer Science, 1994, 2, 350-355), conjugated polymer devices where layers of polymers such as poly(phenylenevinylene) act as the charge carrying and emitting species (see J. J. M. Halls, D. R. Baigent, F. Cacialli, N. C. Greenham, R. H. Friend, S. C. Moratti, and A. B. Holmes, “Light-emitting and Photoconductive Diodes Fabricated with Conjugated Polymers,” Thin Solid Films, 1996, 276, 13-20), vapor deposited small molecule heterostructure devices (see U.S. Pat. No. 5,061,569, incorporated by reference, and C. H. Chen, J. Shi, and C. W. Tang, “Recent Developments in Molecular Organic Electroluminescent Materials,” Macromolecular Symposia, 1997, 125, 1-48), light emitting electrochemical cells (see Q. Pei, Y. Yang, G. Yu, C. Zang, and A. J. Heeger, “Polymer Light-Emitting Electrochemical Cells: In Situ Formation of Light-Emitting p-n Junction,” Journal of the American Chemical Society, 1996, 118, 3922-3929), vertically stacked organic light-emitting diodes capable of emitting light of multiple wavelengths (see U.S. Pat. No. 5,707,745, incorporated by reference, and Z. Shen, P. E. Burrows, V. Bulovic, S. R. Forrest, and M. E. Thompson, “Three-Color, Tunable, Organic Light-Emitting Devices,” Science, 1997, 276, 2009-2011).
Essentially all organic light emitting materials, organic charge transport materials and organic hole transport materials are adversely affected by heat, light, oxygen, and moisture. The low work function metal cathodes typically used in OLEDs are also sensitive to oxygen and moisture, which can cause corrosion and failure of the cathode. It is important, therefore, to protect these layers from exposure to the open air. Some methods of making OEDs such as OLEDs partially protect these layers, for example, methods that use barrier films as substrates, but the top layer of the OLED remains exposed. A separate encapsulation step, such as bonding a metal cap on top of an OLED, is typically required. This separate encapsulation step adds to manufacturing complexity and is not generally suited to the fabrication of flexible OLEDs.